490 



NATURE 



\ April 2 2, 1875 



from the 8th to the 12th of Apri), in a paraboHc orbit. 

 With the period assigned by Burckhardt, the comet would 

 have passed its aphelion in October or November 1763, 

 at which time the planet Jupiter was near the same helio- 

 centric longitude, and his distance from the comet might 

 have been less than 0-4 ; indeed, a period very slightly 

 shorter than Burckhardt's, and quite within the probable 

 error of his determination, might have occasioned an 

 extremely close approach of the two bodies, producing, 

 in all probability, a great alteration of elements, and re- 

 sulting in the ellipse of short period indicated by the 

 observations of 1766. This comet was suspected by 

 Clausen to have been identical with the comet of July 

 1 8 19, or the comet of Winnecke, which has been observed 

 during the present year ; and the very possible close 

 approach to the planet Jupiter in the autumn of 1763 

 may have been the cause of the introduction of this body 

 amongst the quickly revolving comets of the system. It 

 is also to be remarked that" Burckhardt's orbit for 1766 

 points to a close approxim.ation to the orbit of Mercury; 

 in about heliocentric longitude 290°, the distance is less 

 than o'o25. 



THE SOLAR ECLIPSE 



IN continuation of our articles on this subject, we print 

 the following telegrams which have since been 

 received, detailing the results of the observations ; to- 

 gether with some remarks which have appeared in the 

 Tiiiu's concerning them. 



First, with regard to the Siam party we have, from 

 Singapore, April 15, the following Renter's telegram with 

 respect to the results obtained : — ■ 



" Valuable results were obtained by the English ob- 

 servers of the solar eclipse in Siam. Although the sky 

 was hazy, the results by the prismatic camera were good. 

 The spectroscopic cameras failed. Eight good photo- 

 graphs of the corona were taken." 



Next, a Times telegram from Dr. Schuster, at Bangkok, 

 as follows : — • 



" The English observers of the solar eclipse in Siam 

 are remaining a few days at their station to take copies ot 

 photographs obtained. Unavoidable accidents prevented 

 them being on the spot until five days before the eclipse. 

 Owing to the untiring energy of Capt. Loftus, the 

 arrangements were nearly complete, and thus partial 

 success of the expedition secured." 



K ext, a Daily A'lws telegram from the special cor- 

 respondent of that Journal with the expedition at 

 Bangkok :— 



" The results of the English Eclipse Expedition must 

 be considered merely preliminary, this being the first 

 time spectrum photography has been tried. The pris- 

 matic camera shows the rings with protuberances at the 

 edge of the sun, and at least one more ring towards the 

 ultra-violet without protuberances. Eight good photo- 

 graphs of the corona were taken, the exposure varying 

 from two to sixteen seconds." 



It will be observed that in none of these telegrams wjs 

 Dr, Janssen ir.enti oned. It is possible, therefore, that he 

 left Singapore before the arrival of the English Expedi- 

 tion. Be this as it may, he observed the eclipse in Siam, 

 and on Monday last, at the Paris Academy of Sciences, a 

 telegram was read from him to the effect that though the 

 sky was not clear, he obtained results, and that these 

 were confirmatory of those obtained in 1871, so far as 

 they related to the coronal atmosphere. 



The news received from the Camorta party is a sad 

 contrast to the above. The following Reuter's telegram, 

 dated " Calcutta, April 18," will no doubt cause universal 

 regret : — 



" The Indian astronomical party at Camorta were 

 successful in observing the external contacts during the 

 solar eclipse. They failed, however, to obtain photo- 



graphic results, owing to the sky being completely over- 

 cast during totality." 



The Times' comments on the results obtained at Siam 

 are as follows :— 



" Reading the above telegram from Dr. Schuster in 

 connection with that which we published in our second 

 edition on Wednesday last (Nature, April 15, p. 474), 

 we see that two-thirds of the work which the Siam expe- 

 dition went out to do have been successfully accomplished. 

 Photographs giving us the actual shape and many of the 

 conditions of the coronal atmosphere at the present 

 epoch of minimum sun-spots have been secured, and 

 these photographs we shall be able to compare with 

 those taken in India and Java in 1S71 at the time of 

 maximum sun-spots. It is not too much to hope that 

 this comparison may teach us much as to the changes in 

 the solar atmosphere which accompany or are brought 

 about by the changes in the spots — changes which require 

 eleven years or thereabout to run through their cycle. 

 But this, after all, is a trifle compared with another part 

 of the work. Not only was photography pure et simple 

 employed to tell us the shape and other conditions of the 

 solar atmosphere, but photography ///(■.!■ spectroscopy has 

 been utilised to tell us the chemical constitution of the 

 various readings of the sun's surroundings ; and it is in 

 this branch of the work that the most valuable of the 

 announced results have been obtained. The Committee 

 of the Royal Society laid so much stress upon this part 

 of the attack that no less than three instruments were 

 devoted to it by the Siam party alone, the work of each 

 being so arranged that it would supplement that accom- 

 plished by any of the others. 



" A few simple considerations will serve to indicate 

 not only the nature of this part of the work, but how 

 carefully it had been prepared throughout by those 

 upon whom the responsibility of organising the expedi- 

 tions fell. The brilliancy of the corona has varied enor- 

 mously — one, indeed, might almost say impossibly — in 

 various eclipses. The celebrated Otto Struvc, for instance, 

 has placed on record the fact that in one of the eclipses 

 which he observed its brilliancy was almost insupport- 

 able to the naked eye ; other astronomers have made use 

 of expressions equally strong, while it is known that, if 

 those who are fortunate enough to have the opportunity 

 of observing eclipses take the precaution of guarding the 

 eye from the direct light of the sun before its disappear- 

 ance, there is not only light enough from the corona to 

 read by with comfort, but a light surpassing in brilliancy 

 the brightest moonlight we are familiar with in these lati- 

 tudes. This is so far as the eye is concerned. When we 

 deal with the photographic plate instead of the retina, the 

 brilliancy of the corona becomes yet more certain. A 

 camera of, say, four inches aperture will impress an image 

 of the corona on a prepared plate in far less time than it 

 will impress an image of the moon at its brightest. This 

 is one indication of the photographic brilliancy of the 

 coronal light, and in a former article we took occasion to 

 refer to others of an equally striking kind which were 

 rendered very obvious during the eclipse of 1871. The 

 evidence as to the brightness of the spectrum of the 

 lower layers of the sun's atmosphere is equally strong." 



" The Royal Society Committee, therelore, would have 

 been justified in reckoning upon a bright corona. They 

 did so, but at the same time they provided for a very 

 feeble one. Long before the expedition sailed, the 

 members of both parties made some very interesting re- 

 searches on the possibility of securing photographs of 

 gaseous spectra — that is, precisely such spectra as those 

 which it is natural to expect will be furnished to us by the 

 corona. They found that, with a time of exposure only 

 slightly in excess of that allowed by the eclipse itself, they 

 were enabled to phutograjih the spectra of chlorine, 

 nitrogen, and other similar bodies under somewhat com- 

 plicated instrumental conditions, and when those spectra 



